how do i insert a keyframe at the frame where the object reaches a path control point?
Not sure if it helps, but if you don't mind loosing the constraint itself (you can easily restore it if needed anyway) you could bake the action into keyframes.

That way you get an already drawn graphic of the object positions along time, and you get a better visual feedback of where the object is and when.

Keep in mind that this will not automatically give you keyframes and the exact curve control points, but the position graphics might give a rough idea of where tight turns are.

That way you can then easily accelerate and decelerate the animation by nudging frames back or forth in the graph editor.